This invention relates to a method of preparing 3-acylisoxazolines. In particular, this invention relates to a novel method of preparing 3-acylisoxazolines by reacting alkenes with alpha-nitroketones.
Isoxazolines, such as acylisoxazolines, can be prepared by the action of an acid, such as hydrochloric acid on an unsaturated alpha-diketone, monooxime or by reacting an alpah-ethylenic ketone, such as 2-butenone, and a nitrile oxide. The aforementioned methods are not particularly attractive inasmuch as the starting materials are difficult to prepare. Moreover, Quilico et al., Nature, vol. 166, page 226 (1956) and Grundmann and Grunanger, The Nitrile Oxides, Springer-Verlag (1971) describe the preparation of 2-isoxazolines by the 1,3-dipolar cycloaddition of nitrile oxides to alkenes. Nitrile oxides are generally unstable materials and a main difficulty, apart from the threat of explosion, resides in the nitrile oxide's rapid spontaneous polymerization or dimerization to furoxanes. One method for preparing nitrile oxides, such as benzonitrile oxide is by dehydrochlorination of the corresponding hydroximyl acid chloride by the action of an inorganic or organic base in either an aqueous or anhydrous organic medium. Tertiary amines have been evaluated as dehydrochlorinating agents for hydroximic acid chlorides dissolved or supsended in ether, but may react with hydroximic acid chlorides to form stable addition compounds instead of nitrile oxides. The use of two separate reaction stages for rearing isoxazolines is disadvantageous, particularly where the first stage dehydrohalogenation is conducted at a substantially lower temperature than the second stage cycloaddition. Such a procedure involving a plurality of stages conducted at different temperatures results in economic penalties and detracts from the commercial attractiveness of the overall process.
It is therefore an object of this invention to provide a novel method for preparing 3-acylisoxazolines.
Another object of this invention is to provide a method for preparing 3-acylisoxazolines from alphanitroketones and alkenes by a one step reaction.
Yet another object of this invention is to provide a method for preparing 3-acylisoxazolines from materials having long storage lives.
Other objects and advantages will become apparent from the following detailed description and examples.